Vehicles, such as automobiles, off-road vehicles, agricultural tractors, or self-propelled agricultural implements, may be used in a variety of tasks (e.g., to transport people or goods from one location to another, to tow agricultural implements, to harvest, plow, cultivate, spray, etc.). Traditionally, vehicles are manually operated by an operator. That is, the steering and speed of a vehicle are controlled by an operator driving the vehicle. Unfortunately, the operator may not drive the vehicle along an efficient path from one location to another location as compared to autonomously controlled vehicles.
Accordingly, the number of applications for automated ground vehicles has been rapidly increasing. Examples include autonomous mining trucks, tractors, military target vehicles, and durability testing of passenger vehicles. It is convenient to construct desired paths out of tangentially connected circular arc and straight line segments, which have been shown to be optimal in terms of path length. Unfortunately, such paths cannot actually be driven if the steering angle is produced by a servo system, which introduces a finite steering rate causing lag, and most autonomous vehicles typically include rate-limited servo steering systems that have a maximum turning rate.
Previous applications in this area derived schemes for driving such paths under the assumption that transitions between segments were “unplanned.” In these applications, the control system simply switches to a new path segment at some time ahead of actually reaching the transition point. This rudimentary process is one way of dealing with assumptions of linear lag and a nonlinear rate-limited actuator. However, these previous applications may experience path segment transitions as “disturbances” that the control system must continuously overcome, which may lead to control system degradation over time. Furthermore, previous applications may not achieve optimal transitions between path segments.